Lane keeping assist system

ABSTRACT

A lane keeping assist system (LKAS) is equipped with a compensator capable of solving the problem in which video data, which is measured by a video sensor, the processing speed of which is lower than the data processing speed of the LKAS, is repeatedly used, thereby improving the kinematic characteristics of a vehicle and lane-keeping control performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims under 35 U.S.C. §119(a) priority to KoreanApplication No. 10-2007-0129246, filed on Dec. 12, 2007, the disclosureof which is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a lane keeping assist system (LKAS).

2. Related Art

With the improvement of various functions of vehicles, varioustechnologies for improving the safety and comfort of the drivers andpassengers have been introduced. In particular, an LKAS capable ofkeeping a vehicle in a particular lane is close to commercialization.

An LKAS is a system for detecting whether a vehicle deviates from atarget lane and assisting a driver in remaining in the target lane at adesired speed. In order to implement this, the target lane and thekinematic characteristics of the vehicle must be measured in real time,and appropriate control must be performed based on the results of themeasurement.

In a prior art LKAS, the video data processing speed of a video sensoris lower than the data processing speed of the LKAS. Because of this,the prior art LKAS does not perform the function in a reliable manner.

For example, when the data processing period of the system is 10 ms andthe video data frame measurement period of the video sensor is 50 ms,the system receives new video data from the video sensor every 50 ms inthe processing of data, and thus the system repeatedly uses previousvideo data for 40 ms (four periods). As a result, the system has aproblem in that the system cannot appropriately control the traveling ofa vehicle because the same video data is used for five instances of dataprocessing.

Of course, in the case of a high-performance video sensor, the dataprocessing speed thereof can be synchronized with the data processingspeed of a system, and thus the lane keeping function may be improved.However, since the high-performance video sensor is expensive, the useof the high-performance sensor increases manufacturing costs.

FIG. 1 is a diagram showing variables indicative of the kinematiccharacteristics of a vehicle. Referring to FIG. 1, the control variablesof a lane keeping assist system that must be taken into account when avehicle travels along a curved lane will be described below.

An LKAS enables a vehicle to remain in a lane the vehicle is travelingby measuring or estimating a velocity V of the vehicle, a lateralvelocity ν, a yaw rate γ, a required forward angle δ_(f) and a slideslip angle β, a deviation angle θ_(p) at a measuring point, and adeviation distance y_(p) at the measuring point, outputting a steeringmotor torque based on the results of the measurement or estimation, andtransmitting a drive signal related to the torque to the steering motor.

FIG. 2 is a graph illustrating the lane following performance of theprior art LKAS, and FIG. 3 is a graph illustrating the lane followingperformance based on video detection speeds of the video sensor of theprior art LKAS.

Referring to FIG. 2, a problem arises in that the system cannot followthe traveling characteristics of a vehicle in real time due to therepeated use of data that is measured by the video sensor. Accordingly,the vehicle controlled by the system cannot be accurately kept in itslane and has a certain error value.

FIG. 3 shows that an error in the deviation distance (e.g.,approximately 10 cm) may occur when the data processing period of avideo sensor is 50 ms and the data processing period of a system is 10ms.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide an LKAS that is equipped with a compensatorcapable of estimating a deviation angle θ_(p) of a vehicle and adeviation distance y_(p) based on the kinematic characteristics ofvehicle.

In order to accomplish the above object, the present invention, in oneaspect, provides an LKAS including a video sensor unit, a sensor unit, acontrol unit, and a compensation unit. The video sensor unit capturesvideo image or images outside of a vehicle and measuring locationinformation of the vehicle and a curvature ρ_(p) of a lane. The(variable) sensor unit measures a variable value or values related toone or more kinematic characteristics of the vehicle. The control unitperforms lane keeping control based on the location information of thevehicle, the curvature of the lane and the variable value or valuesrelated to the kinematic characteristics. The compensation unitestimates a deviation angle θ_(p) and a deviation distance y_(p) basedon data from the video sensor unit, the sensor unit and the control unitin a period that is a control data processing period of the control unitbut is not a measurement period of the video sensor unit, and transmitsthe estimated values to the control unit.

In this case, the location information of the vehicle measured by thevideo sensor unit may be a deviation angle θ_(p) and a deviationdistance y_(p) of the vehicle with respect to a measuring point.

The variable value or values related to the kinematic characteristicsmay be a velocity V of the vehicle, a yaw rate γ and a required forwardangle δ_(f) measured by the sensor unit 20, or a combination thereof.

Furthermore, the data transmitted from the video sensor unit, the sensorunit and the control unit 40 to the compensation unit may include atlease one of a deviation angle θ_(p) and a deviation distance y_(p)measured by the video sensor unit 10, a velocity V and a yaw rate γmeasured by the sensor unit, and a lateral velocity ν estimated by thecontrol unit. In detail, the deviation distance estimated by thecompensation unit may be y_(p)=∫(ν+L_(p)×γ+V×θ_(p))dt (where L_(p) is adistance between a measuring point of the video sensor and a centralaxis of the vehicle), and the estimated deviation angle θ_(p) by thecompensation unit may be θ_(p)=∫(γ−V×ρ)dt, where ρ is a curvature of aroad.

In this case, the control unit may calculate a torque value T_(m) of asteering motor of the vehicle using the following state equation, andperform control function so that the vehicle remains in a target lane:

$\begin{bmatrix}{\overset{¨}{\delta}}_{f} \\{\overset{.}{\delta}}_{f} \\\overset{.}{\gamma} \\\overset{.}{v} \\{\overset{.}{\theta}}_{p} \\{\overset{.}{y}}_{p}\end{bmatrix} = {{\begin{bmatrix}{- \frac{C_{s}}{I_{s}}} & {- \frac{\xi\; C_{t}}{I_{s}}} & \frac{\xi\; C_{f}L_{f}}{I_{s}V} & \frac{\xi\; C_{f}}{I_{s}V} & 0 & 0 \\1 & 0 & 0 & 0 & 0 & 0 \\0 & \frac{C_{f}I_{f}}{I_{s}} & {- \frac{{C_{f}L_{f}^{2}} + {C_{r}L_{r}^{2}}}{I_{s}V}} & {- \frac{{C_{f}L_{f}} - {C_{r}L_{r}}}{I_{s}V}} & 0 & 0 \\0 & \frac{C_{f}}{m} & {{- V} - \frac{{C_{f}L_{f}} - {C_{r}L_{r}}}{m\; V}} & {- \frac{C_{f} + C_{r}}{m\; V}} & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 \\0 & 0 & L_{p} & 1 & V & 0\end{bmatrix}\left\lbrack \begin{matrix}{\overset{.}{\delta}}_{f} \\\delta_{f} \\\gamma \\v \\\theta_{p} \\y_{p}\end{matrix} \right\rbrack} + {\begin{bmatrix}\frac{N_{m}}{I_{s}} \\0 \\0 \\0 \\0 \\0\end{bmatrix}T_{m}} + {\begin{bmatrix}\frac{N_{s}}{I_{s}} & 0 \\0 & 0 \\0 & 0 \\0 & 0 \\0 & {- V} \\0 & 0\end{bmatrix}\begin{bmatrix}T_{h} \\\rho_{p}\end{bmatrix}}}$ $y = {{Cx} = {\begin{bmatrix}\theta_{p} \\y_{p}\end{bmatrix} = {\begin{bmatrix}0 & 0 & 0 & 0 & 1 & 0 \\0 & 0 & 0 & 0 & 0 & 1\end{bmatrix}x}}}$where C_(s) represents a damping value of the steering system of thevehicle, I_(s) represents an inertia moment of the steering system, ξrepresents a contact distance of wheels, C_(f) represents a corneringstiffness value of the front wheels of the vehicle, L_(f) represents adistance from the center of gravity of the vehicle to the front wheelaxis, C_(r) represents a cornering stiffness value of the rear wheels ofthe vehicle, L_(r) represents a distance from the center of gravity ofthe vehicle to the rear wheel axis, m represents the weight of thevehicle, N_(m) represents a gear ratio of the motor of the vehicle,N_(s) represents a steering ratio of an actual steering device, T_(h)represents a torque of a steering wheel of the vehicle, and ρ_(p)represents a curvature of a lane.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

The above and other features of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram showing variables indicative of the kinematiccharacteristics of a vehicle;

FIG. 2 is a graph illustrating the lane following performance of theprior art LKAS;

FIG. 3 is a graph illustrating the lane following performance based onvideo detection speeds of the video sensor of the prior art LKAS;

FIG. 4 is a conceptual diagram of an LKAS according to the presentinvention;

FIG. 5 is a graph showing the lane following performance of an LKASaccording to an embodiment of the present invention; and

FIG. 6 is a graph comparing the lane following performance of the LKASequipped with a compensator according to the present invention with thatof the prior art LKAS.

DETAILED DESCRIPTION

Hereinafter reference will now be made in detail to various embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings and described below, in which the same referencenumerals are used to designate the same or similar components.

FIG. 4 is a conceptual diagram showing an LKAS according to the presentinvention. Referring to FIG. 4, the LKAS according to the presentinvention includes a video sensor unit 10, a sensor unit 20, acompensation unit 30, and a control unit 40.

The video sensor unit 10 captures video image or images outside of avehicle, and creates video image information. In greater detail, thevideo sensor unit 10 measures a deviation angle θ_(p) at a measuringpoint, a deviation distance y_(p) and a lane curvature ρ_(p) through thecaptured video image information (see FIG. 1).

In this case, since the data processing speed of the video sensor unit10 is lower than the data processing speed of the control unit 40 asdescribed above, it is necessary to appropriately compensate for thedeviation angle θ_(p) and the deviation distance y_(p).

The sensor unit 20 measures a kinematic characteristic variable orvariables of the vehicle necessary for lane-keeping control. In greaterdetail, the sensor unit 20 measures a velocity V of the vehicle, a yawrate γ and a required forward angle δ_(f). Here, the data processingspeed of the sensor unit 20 is the same as that of the control unit 40.

The compensation unit 30 estimates the deviation angle θ_(p) and thedeviation distance y_(p) in conformity with the processing speed of thecontrol unit 40 based on the data measured by the video sensor unit 10and the sensor unit 20 to be synchronized with the data processing speedof the control unit 40. That is, the compensation unit 30 estimates thedeviation angle and the deviation distance during periods correspondingto the difference between the data processing speed of the video sensor10 and the data processing speed of the control unit 40.

For clarity, the deviation angle and the deviation distance measured bythe video sensor 10 are respectively referred to as the ‘measureddeviation angle’ and the ‘measured deviation distance.’ Meanwhile, thedeviation angle and the deviation distance estimated by the compensationunit 30 are respectively referred to as the ‘estimated deviation angle’and the ‘estimated deviation distance.’

The estimated deviation distance and the estimated deviation angle andcan be obtained by the following Equations 1 and 2, respectively.y _(p)=∫(ν+L _(p) ×γ+V×θ _(p))dt   (1)θ_(p)=∫(γ−V×ρ)dt   (2)

That is, according to Equation 1, the estimated deviation distance isthe sum of the deviation distance y_(p)=∫νdt estimated based on thelateral velocity ν of a vehicle, the deviation distancey_(p)=∫(L_(p)×γ)dt estimated based on the yaw rate γ of the vehicle, andthe deviation distance y_(p)=∫(V×θ_(p))dt estimated base on thedistortion of the vehicle.

Here, L_(p) is a distance between the measuring point of the videosensor 10 and the central axis of the vehicle, which is a constant.

Furthermore, the deviation angle in the equation with regard to thedeviation distance estimated based on the distortion of the vehicle is ameasured deviation angle measured by the video sensor 10.

According to Equation 2, the estimated deviation angle is the sum of thedeviation angle θ_(p)=∫γdt estimated based on the yaw rate and thedeviation angle θ_(p)=∫(−V×ρ)dt estimated based on a road curvature ρ.

Here, the road curvature represents a curvature measured by the videosensor 10.

The control unit 40 performs lane-keeping control based on the kinematiccharacteristics of the vehicle measured by the video sensor unit 10 andthe sensor unit 20 and the estimated deviation angle and the estimateddeviation distance compensated for by the compensation unit 30. Thecontrol unit 40 involves a control state equation shown in the followingEquation 3.

$\begin{matrix}{{\begin{bmatrix}{\overset{¨}{\delta}}_{f} \\{\overset{.}{\delta}}_{f} \\\overset{.}{\gamma} \\\overset{.}{v} \\{\overset{.}{\theta}}_{p} \\{\overset{.}{y}}_{p}\end{bmatrix} = {{\begin{bmatrix}{- \frac{C_{s}}{I_{s}}} & {- \frac{\xi\; C_{t}}{I_{s}}} & \frac{\xi\; C_{f}L_{f}}{I_{s}V} & \frac{\xi\; C_{f}}{I_{s}V} & 0 & 0 \\1 & 0 & 0 & 0 & 0 & 0 \\0 & \frac{C_{f}I_{f}}{I_{s}} & {- \frac{{C_{f}L_{f}^{2}} + {C_{r}L_{r}^{2}}}{I_{s}V}} & {- \frac{{C_{f}L_{f}} - {C_{r}L_{r}}}{I_{s}V}} & 0 & 0 \\0 & \frac{C_{f}}{m} & {{- V} - \frac{{C_{f}L_{f}} - {C_{r}L_{r}}}{m\; V}} & {- \frac{C_{f} + C_{r}}{m\; V}} & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 \\0 & 0 & L_{p} & 1 & V & 0\end{bmatrix}\left\lbrack \begin{matrix}{\overset{.}{\delta}}_{f} \\\delta_{f} \\\gamma \\v \\\theta_{p} \\y_{p}\end{matrix} \right\rbrack} + {\begin{bmatrix}\frac{N_{m}}{I_{s}} \\0 \\0 \\0 \\0 \\0\end{bmatrix}T_{m}} + {\begin{bmatrix}\frac{N_{s}}{I_{s}} & 0 \\0 & 0 \\0 & 0 \\0 & 0 \\0 & {- V} \\0 & 0\end{bmatrix}\begin{bmatrix}T_{h} \\\rho_{p}\end{bmatrix}}}}{y = {{Cx} = {\begin{bmatrix}\theta_{p} \\y_{p}\end{bmatrix} = {\begin{bmatrix}0 & 0 & 0 & 0 & 1 & 0 \\0 & 0 & 0 & 0 & 0 & 1\end{bmatrix}x}}}}} & (3)\end{matrix}$

where C_(s) represents a damping value of the steering system of thevehicle, I_(s) represents an inertia moment of the steering system, ξrepresents a contact distance of wheels, C_(f) represents a corneringstiffness value of the front wheels of the vehicle, L_(f) represents adistance from the center of gravity of the vehicle to the front wheelaxis, C_(r) represents a cornering stiffness value of the rear wheels ofthe vehicle, L_(r) represents a distance from the center of gravity ofthe vehicle to the rear wheel axis, m represents the weight of thevehicle, N_(m) represents a gear ratio of the motor of the vehicle,N_(s) represents a steering ratio of an actual steering device, T_(h)represents a torque of a steering wheel of the vehicle, and ρ_(p)represents a curvature of a lane.

The velocity V of the vehicle and the torque T_(h) of the steering wheelare measured by the sensor unit 20. The lane curvature ρ_(p) isestimated by the observation device included in the control unit 40. Theremaining values are constants that are predetermined depending on thetype of vehicle.

From Equation 3, the control unit 40 calculates a torque value of thesteering motor of the vehicle. More particularly, the control unit 40calculates a torque value T_(m) of the steering motor, which makes thevalues of the deviation angle and the deviation distance, among thevalues of the state variables of Equation 3, become zero.

Here, it is impossible to measure the lateral velocity of the vehicle,and the lateral velocity is estimated through an observation deviceincluded in the control unit 40.

Furthermore, the deviation angle θ_(p) and the deviation distance y_(p)are the measured deviation angle and the measured deviation distancemeasured by the video sensor unit 10, or the estimated deviation angleand the estimated deviation distance measured by the compensation unit30.

Preferably, the control unit 40 performs lane-keeping control using thedeviation angle and the deviation distance measured by the video sensorunit 10 in case where its period is the same as that of the video sensorunit 10 (for example, 50 ms, 100 ms, 150 ms, . . . ), and performslane-keeping control using the deviation angle and the deviationdistance estimated by the compensation unit 30 in case where it is notthe same as the period of the video sensor unit 10 (for example, 10 ms,20 ms, 30 ms, 40 ms, 60 ms, . . . ).

FIG. 5 is a graph showing the lane following performance of the LKASaccording to the present invention. From FIG. 5, it can be seen thatlane keeping control performance is improved in the case in which thedeviation angles and deviation distances, measured by the video sensorunit 10 of the vehicle, and the deviation angles and deviationdistances, estimated by the compensation unit 30, are used.

FIG. 6 is a graph comparing the lane following performance of the LKASequipped with a compensator according to the present invention with thatof the prior art LKAS. From FIG. 6, it can be seen that in the LKASaccording to the present invention, the deviation distance error isreduced by about 10 cm in spite of the fact that the processing periodof the video sensor unit 10 is 50 ms.

As described above, the lane keeping control performance can besignificantly improved by estimating the deviation angles and thedeviation distances, which cannot be obtained by the video sensor, usinganother kinematic characteristic equation.

According to the present invention, data measured by a video sensorhaving a inexpensive low data processing speed can be compensated for soas to keep a vehicle in a target lane, with the result that the safetyand comfort can be improved and manufacturing costs can be reduced.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A lane-keeping assist system (LKAS) for a vehicle, comprising: avideo sensor unit for capturing video image or images outside of thevehicle and measuring location information of the vehicle and acurvature (ρ_(p)) of a lane with respect to a measuring point; a sensorunit for measuring a variable value or values related to one or morekinematic characteristics of the vehicle; a control unit for performinglane keeping control based on the location information, the lanecurvature and the variable value or values related to the kinematiccharacteristics; and a compensation unit for estimating a deviationangle (θ_(p)) and a deviation distance (y_(p)) based on data from thevideo sensor unit, the sensor unit and the control unit in a period thatis a control data processing period of the control unit but is not ameasurement period of the video sensor unit, and transmitting theestimated values to the control unit.
 2. The LKAS as set forth in claim1, wherein the location information of the vehicle measured by the videosensor unit is a deviation angle (θ_(p)) and a deviation distance(y_(p)) of the vehicle with respect to the measuring point.
 3. The LKASas set forth in claim 1, wherein the variable value related to thekinematic characteristics is a velocity (V) of the vehicle, a yaw rate(γ), a required forward angle (δ_(f)) measured by the sensor unit 20, ora combination thereof.
 4. The LKAS as set forth in claim 1, wherein thedata transmitted from the video sensor unit, the sensor unit and thecontrol unit 40 to the compensation unit comprises at least one selectedfrom the group consisting of a deviation angle (θ_(p)) and a deviationdistance (y_(p)) measured by the video sensor unit 10, a velocity (V) ofthe vehicle and a yaw rate (γ) measured by the sensor unit, and alateral velocity (ν) estimated by the control unit.
 5. The LKAS as setforth in claim 1, wherein the deviation distance estimated by thecompensation unit is obtained by the equationy_(p)=∫(ν+L_(p)×γ+V×θ_(p))dt where ν is a lateral velocity, L_(p) is adistance between a measuring point of the video sensor and a centralaxis of the vehicle, γ is a yaw rate of the vehicle, V is a velocity ofthe vehicle and the estimated deviation angle by the compensation unitis obtained by the equation θ_(p)=∫(γ−V×ρ)dt where ρ is a curvature of aroad.
 6. The LKAS as set forth in any one of claims 1, wherein thecontrol unit calculates a torque value T_(m) of a steering motor of thevehicle using the following state equation and performs control so thatthe vehicle is kept in a target lane: $\begin{bmatrix}{\overset{¨}{\delta}}_{f} \\{\overset{.}{\delta}}_{f} \\\overset{.}{\gamma} \\\overset{.}{v} \\{\overset{.}{\theta}}_{p} \\{\overset{.}{y}}_{p}\end{bmatrix} = {{\begin{bmatrix}{- \frac{C_{s}}{I_{s}}} & {- \frac{\xi\; C_{t}}{I_{s}}} & \frac{\xi\; C_{f}L_{f}}{I_{s}V} & \frac{\xi\; C_{f}}{I_{s}V} & 0 & 0 \\1 & 0 & 0 & 0 & 0 & 0 \\0 & \frac{C_{f}I_{f}}{I_{s}} & {- \frac{{C_{f}L_{f}^{2}} + {C_{r}L_{r}^{2}}}{I_{s}V}} & {- \frac{{C_{f}L_{f}} - {C_{r}L_{r}}}{I_{s}V}} & 0 & 0 \\0 & \frac{C_{f}}{m} & {{- V} - \frac{{C_{f}L_{f}} - {C_{r}L_{r}}}{m\; V}} & {- \frac{C_{f} + C_{r}}{m\; V}} & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 \\0 & 0 & L_{p} & 1 & V & 0\end{bmatrix}\left\lbrack \begin{matrix}{\overset{.}{\delta}}_{f} \\\delta_{f} \\\gamma \\v \\\theta_{p} \\y_{p}\end{matrix} \right\rbrack} + {\begin{bmatrix}\frac{N_{m}}{I_{s}} \\0 \\0 \\0 \\0 \\0\end{bmatrix}T_{m}} + {\begin{bmatrix}\frac{N_{s}}{I_{s}} & 0 \\0 & 0 \\0 & 0 \\0 & 0 \\0 & {- V} \\0 & 0\end{bmatrix}\begin{bmatrix}T_{h} \\\rho_{p}\end{bmatrix}}}$ $y = {{Cx} = {\begin{bmatrix}\theta_{p} \\y_{p}\end{bmatrix} = {\begin{bmatrix}0 & 0 & 0 & 0 & 1 & 0 \\0 & 0 & 0 & 0 & 0 & 1\end{bmatrix}x}}}$ where C_(s) represents a damping value of thesteering system of the vehicle, I_(s) represents an inertia moment ofthe steering system, ξ represents a contact distance of wheels, C_(f)represents a cornering stiffness value of the front wheels of thevehicle, L_(f) represents a distance from the center of gravity of thevehicle to the front wheel axis, C_(r) represents a cornering stiffnessvalue of the rear wheels of the vehicle, L_(r) represents a distancefrom the center of gravity of the vehicle to the rear wheel axis, mrepresents the weight of the vehicle, N_(m) represents a gear ratio ofthe motor of the vehicle, N_(s) represents a steering ratio of an actualsteering device, T_(h) represents a torque of a steering wheel of thevehicle, and ρ_(p) represents a curvature of a lane.